WP Change The Role

<?php
/*
Plugin Name: Change The Role
Plugin URI: https://ja.forums.wordpress.org/topic/141608
Version: 0.1a.20141031
Author: mizube
Author URI: https://ja.forums.wordpress.org/profile/419438
Text Domain: change-the-role
Domain Path: /languages/
Description: Enables users to change the user role in some roles.
*/

add_action( 'plugins_loaded', array( 'ChangeTheRole', '__boot' ) );
register_deactivation_hook( __FILE__, array( 'ChangeTheRole', 'deactivated' ) );

class ChangeTheRole {

    public $textdomain = 'change-the-role';

    public static function __boot() {
        $class = __CLASS__;
        new $class();
    }

    public function __construct() {
        load_plugin_textdomain( $this->textdomain, false, basename( dirname( __FILE__ ) ) . '/languages/' );

        add_action( 'personal_options_update', array( $this, 'action_personal_options_update' ) );
        add_action( 'personal_options', array( $this, 'action_personal_options' ) );
        add_action( 'admin_init', array( $this, 'action_admin_init' ) );
    }

    public function action_personal_options_update( $user_id ) {
        if ( !$user_id || !isset( $_POST['erc_role'] ) || !current_user_can( 'edit_user', $user_id ) )
            return;

        $erc_roles = get_option( 'erc_changeable_roles', array() );
        $erc_role  = sanitize_text_field( $_POST['erc_role'] );

        if ( !in_array( $erc_role, $erc_roles ) )
            return;

        $user_roles = get_userdata( $user_id )->roles;
        $has_roles  = false;

        foreach ( $user_roles as $user_role ) {
            if ( in_array( $user_role, $erc_roles ) ) {
                $has_roles = true;
                break;
            }
        }

        if ( !$has_roles ) return;

        $wp_user = new WP_User( $user_id );
        $wp_user->set_role( $erc_role );
        unset( $wp_user );
    }

    public function action_personal_options( $profileuser ) {
        global $wp_roles;

        $role_names = $wp_roles->get_names();
        $erc_roles  = get_option( 'erc_changeable_roles', array() );
        $has_roles  = false;

        foreach ( $profileuser->roles as $user_role ) {
            if ( in_array( $user_role, $erc_roles ) ) {
                $has_roles = true;
                break;
            }
        }

        if ( !empty( $erc_roles ) && $has_roles && !current_user_can( 'edit_users' ) ) {
            echo '<table class="form-table"><tr><th scope="row"><label for="erc_role">' . __( 'Role' ) . '</label></th><td>';
            echo '<select name="erc_role" id="erc_role">';
            foreach ( $erc_roles as $role ) {
                echo '<option value="' . $role . '"'
                    . selected( in_array( $role, $profileuser->roles ), true, false ) . '>'
                    . translate_user_role( $role_names[$role] ) . '</option>';
            }
            echo '</select>';
            echo '</td></tr></table>';
        }
    }

    public function action_admin_init() {
        add_settings_field(
            'erc_changeable_roles',
            __( 'Changeable Roles', $this->textdomain ),
            array( $this, 'callback_render_roles_list' ),
            'general',
            'default'
        );
        register_setting( 'general', 'erc_changeable_roles' );
    }

    public function callback_render_roles_list() {
        global $wp_roles;
        $roles  = $wp_roles->get_names();
        $option = get_option( 'erc_changeable_roles', array() );
        echo '<ul>';
        foreach ( $roles as $role => $label ) {
            if( isset( $wp_roles->roles[$role]['capabilities']['manage_options'] ) ) continue;
            echo '<li><label><input type="checkbox" name="erc_changeable_roles[]" value="' . $role . '" '
                . checked( in_array( $role, $option ), true, false ) . ' /> '
                . translate_user_role( $label ) . '</label></li>';
        }
        echo '</ul>';
    }

    public static function deactivated() {
        delete_option( 'erc_changeable_roles' );
    }
}